Hot water Secondary return quires, 5 bathrooms

[Knee pads]

Hello I'm after advice on the installation of a secondary hot water system . The system will be suppling five bathroom s, a kitchen , cloakroom and utility room in a barn conversion. I usually install on a small domestic level so this is a bit bigger than the norm.
The hot water and heating system is being installed my a renewables company . They propose to install a 500 litre unvented cylinder and accumulator .
I'm just doing the first fix for the bathrooms and the rest of the plumbing in the property . This system will definitely need a secondary hot return system.


My query is with the pipe sizing.


I'm proposing to install 35 MM hot flow from the cylinder up to the first two bathrooms ( individual hot bathroom supply's 22 MM ) , then reduce down to 28 MM for the remaining three bathrooms .
The secondary return will be in 28 MM from the cylinder and reduce down as required by the last bathroom.
I intend to install locksheild valves on the returns at the outlets for balancing and fully insulate all pipe work.


Am I right with 35mm hot pipe work or will 28 MM be enough?

 

[ShaunCorbs]

please get a decent plumber who knows about secondary returns as your wrong/ there wrong

 

[Knee pads]

Thanks for the input?!

 

[ShaunCorbs]

ok simple 15mm from each bathroom to the cylinder

22mm manifold

lcokshield valve on each 15mm

 

[Subby]

22mm on a secondary return with a bronze pump. Stab off in 15mm for each outlet and have the return as close to each outlet as practical

 

[Subby]

And make sure it's all lagged correctly

 

[joni os]

Much depends on usage and anticipated performance. Put it back to client for design and work to an agreed specification. Whoever sized the unvented and heating should have done the figures.

 

[ShaunCorbs]

the renewable's company should tell you what they require

 

[Knee pads]

Ok thanks

 

[CHRISX]

Hello I'm after advice on the installation of a secondary hot water system . The system will be suppling five bathroom s, a kitchen , cloakroom and utility room in a barn conversion. I usually install on a small domestic level so this is a bit bigger than the norm.
The hot water and heating system is being installed my a renewables company . They propose to install a 500 litre unvented cylinder and accumulator .
I'm just doing the first fix for the bathrooms and the rest of the plumbing in the property . This system will definitely need a secondary hot return system.


My query is with the pipe sizing.


I'm proposing to install 35 MM hot flow from the cylinder up to the first two bathrooms ( individual hot bathroom supply's 22 MM ) , then reduce down to 28 MM for the remaining three bathrooms .
The secondary return will be in 28 MM from the cylinder and reduce down as required by the last bathroom.
I intend to install locksheild valves on the returns at the outlets for balancing and fully insulate all pipe work.


Am I right with 35mm hot pipe work or will 28 MM be enough?

Hello Knee pads,

As has been mentioned already by another Member it is VITAL that the Hot water supply and Secondary return is really well insulated - I would state to a `Professional standard` - or any significant Heat loss will fairly quickly dissipate all of the Hot water in the Cylinder - even from a 500 litre one.

I also agree with a Members suggestion that You should be going back to the Renewables Company to have them specify the design / pipe sizing for the Hot water supply and Secondary return.

It is very easy for this type of thing to go wrong and it would usually only be found out after the job was nearly finished / all of the Bathrooms - Kitchen - Utility etc. already installed !


Having said that here are a couple of comments on what You wrote:

You don`t need anything like a 28mm return - the return pipe is only to keep the Hot Water circulating around the 35mm supply pipe so that it is available reasonably quickly to each Hot water outlet in the property.

However You MUST make sure that you Tee off the 35mm / 28mm in such a way that the Hot water is not being drawn form the return pipe.

A 22mm or even a 15mm return pipe depending on how the pipework will be run - will allow the Hot water from the Cylinder to circulate around the property so that it is available quickly at each outlet - but of course you must make sure that there is no `dead heading` when the various secondary returns meet each other / tee in.


You will be trying to circulate the Hot water slowly - as even when correctly insulated while it is circulating it will still be losing some heat.

I am sure that you know there should also be a Programmer or Timeswitch controlling the Pump to allow time setting of the Hot water Secondary circulation - depending on the proposed Hot water usage times.

I have often seen properties where the Hot water demand / Secondary circulation was causing the Cylinder to have to be heated almost constantly - however perhaps the owners of the 5 Bathroom property that you described will not be worried about something like that.



I would urge You to definitely get the Renewables Company to specify what they want you to install - on a job such as you describe it should never be `Fit it and hope`.


I don`t mean anything patronising by that comment - when Plumbing is `upsized` from the normal Domestic Home to supply anything like 5 Bathrooms - Kitchen - Utility & Cloakroom the correct calculations are definitely required.

When calculating pipe sizes for multiple Bathrooms there are `probable usage` factors that are supposed to be used - basically guessing the likelihood of how many Bathrooms / Hot & Cold outlets would be being used at the same time.

However calculating on a `probable use` basis can really backfire if the Householders / Family do use each Bathroom at the same time every day !


And calculating pipe sizes has to take into consideration the `Resistance Factors` of the pipe lengths and fittings which as you know can have a considerable effect on the Flow rate available - especially in a 5 Bathroom property.

To calculate the Resistance in the `Main pipe runs` and the branches to the outlets you would need to know what pipe size and the length of the pipe runs plus the amount of fittings / elbows - then as in calculating Gas pipe sizes you would work out the `Equivalent Length`- length of pipe plus the resistance factor of each elbow / tee [from a Table of resistance factors].

After calculating all of the pipe runs resistance factors you need to calculate the pressure / flow rate within the Main pipe runs and be able to establish if the volume is sufficient to be able to supply all of the branches / outlets simultaneously.

This is FAR from an easy task and should NOT be falling on your shoulders !



I hope that reading this as well as other Members comments will urge You to seek specifications for the Hot - Cold and Secondary return pipe sizes from the Renewables Company.


Chris

 

[Knee pads]

Thanks Chris for your very informative reply. I was never going to throw myself head first into this job and I'll definitely be putting the design of the system back to the renewables firm.

 

[Chalked]

Fantastic reply there by chrisx

 

[CHRISX]

Fantastic reply there by chrisx

Hello Chalked,

Thank You very much for the compliment - I value the opinion of a fellow Professional.

Thanks also to Members APPlumbing, fezster and fernandoraul for your `Likes`.

Chris

 

[CHRISX]

Thanks Chris for your very informative reply. I was never going to throw myself head first into this job and I'll definitely be putting the design of the system back to the renewables firm.

Hello again Knee pads,

I am glad to hear that You will be going back to the Renewables Company for design details.


I was hoping that my message and other Members comments would have that effect - it would be very easy to miscalculate if you are not used to designing / sizing pipework for a property of this size / with 5 Bathrooms, Kitchen, Utility & Cloakroom.


Please make sure that you inform the Company that the pipe routes and fixings MUST allow for pipe insulation to a really good standard - they should also be specifying the correct rated Armaflex pipe insulation - or very similar specification pipe insulation.

Even the correct Pipe insulation should be calculated / specified to prevent as much Heat loss as possible - fitting the pipe insulation can be more difficult than running the pipework to make a really good job of it - correctly mitred joints / glued etc.

Installing 35mm and 28mm pipework in a House will take some route planning as notching average sized joists will not be possible - that is without allowing for the pipe insulation !

These larger pipe sizes / pipe insulation / pipe routes should ideally have been designed into the Building refurbishment plans - just `accommodating` them as almost an afterthought could cause a lot of problems for the Installer / You.

However - Good luck with the Installation works - it will be good experience.


Chris

 

[fezster]

What is the correct way to apply pipe insulation when pipes are notched through joists? The consensus from most installers is that they not insulate where the notch is, but I can imagine that leads to massive heat loss at every one of those. Or is that just a compromise you have to live with?

 

[CHRISX]

What is the correct way to apply pipe insulation when pipes are notched through joists? The consensus from most installers is that they not insulate where the notch is, but I can imagine that leads to massive heat loss at every one of those. Or is that just a compromise you have to live with?

Hello fezster,

When 28mm & 22mm pipes are notched through joists you really don`t have much choice - you usually cannot enlarge the notches to deepen them because the notches will probably have already exceeded the `one eighth of the depth of the joist` [please excuse my old school measurement] in the case of 28mm pipework or already be about the correct depth in the case of 22mm.

You obviously cannot notch joists to accommodate the pipe insulation - not even a piece across the top of the pipe.


This is particularly significant with long runs of Hot water pipework - or Hot water supply circulation - there would be an undesirable amount of Heat loss.

Applying pipe insulation after pipework has been installed without the insulation having been allowed for in the installation process - or when it cannot be allowed for - e.g. where running through joist notches - the insulation is applied between the joists - and as to be accepted as the compromise that You stated - `better than not insulating at all`.

Installing pipework of 28mm / 35mm and above which has been planned to be correctly insulated - correct wall thickness / mitred joints / glued seams etc. means that the pipe routes have to be designed to avoid notching joists for example - as You can imagine these routes have to be designed / built through the Building specifically to accommodate the pipework and insulation.

That means that the pipe routes have to be built into the Building and are very often not the most direct route to the Bathrooms , Kitchen etc. - this sometimes means that pipes have to be upsized to counter the resistance created by multiple elbow fittings etc. used to run a `roundabout route`.

Chris

 

[plumb_know]

Hi Chrisx,

Thanks for your detailed explanations i try to come on here to develop/reinforce my knowledge when i can and members such as yourself really do make it worth while. i was just wondering if you could provide me with a little more detail on what you would determine as the correct way to tee into the pipework to stop drawing in off the hot water secondary return.

i have not much experience of secondary hot water returns but have been coming across it more often and will likely need to install some in the near future with some of my most recent customers houses.

A diagram or references to good book you would recommend would be great, not that i get much time to read.

All the best

 

[CHRISX]

Hi Chrisx,

Thanks for your detailed explanations i try to come on here to develop/reinforce my knowledge when i can and members such as yourself really do make it worth while. i was just wondering if you could provide me with a little more detail on what you would determine as the correct way to tee into the pipework to stop drawing in off the hot water secondary return.

i have not much experience of secondary hot water returns but have been coming across it more often and will likely need to install some in the near future with some of my most recent customers houses.

A diagram or references to good book you would recommend would be great, not that i get much time to read.

All the best

Hello plumb_know,

This can be hard to describe in writing but I will try to describe the most basic / ideal method.

I don`t know of any Plumbing books that describe this specifically - You could try looking online - Google something like `Hot Water circulation systems` or `Secondary Hot Water circulation` - you might find something that way.

As You know `a picture says a thousand words` - so a diagram would be much better than any written description that I can compose.


This system that I describe would be for a Hot water supply with a Secondary return to circulate Hot water so that it was available quickly at the taps / outlets - but not `instantaneously`:

This means that the Secondary returns do not connect close to the taps - a circuit of Hot water would be flowing around each floor but the pipework from the Supply pipe to the Bathrooms / Kitchens Taps / outlets etc. teed off that so there was a short non-circulated section of pipe in which the water would cool down between uses.

This is usually acceptable if there is only a short run from the Hot water Supply pipe to the Taps / outlets - for example if the Supply pipe is running along a landing with the Bathroom supply teeing off for Taps / Shower perhaps only 4 or 5 metres away.

The ideal situation for Hot water supply with a Secondary return would be that the Hot supply was run from the Cylinder around each floor teeing off to the outlets - with a section of the supply pipe [larger size pipe] extending past the last outlet tee by about a metre [my way of doing it] and then reduced down where the Secondary return pipe is connected to the end of the run - the Secondary return then runs back to the Bronze Pump / Cylinder connection.

The Secondary return from other Floors / parts of the Building are connected in before the Pump.

So basically there is a Hot water supply pipe for each floor / section of the Building which is run adjacent to each Bathroom / Kitchen / Utility room etc.

The Hot water supply to each Bathroom / Kitchen is teed off that and at the END of each Hot water supply run you extend the pipe about a metre past the last tee [my way of doing it] and reduce down to connect the Secondary return [smaller pipe] which runs back to the Bronze Pump / Cylinder.

If a property layout means that the Hot water pipework from the Hot water supply into the Bathrooms / Kitchen / Utility room etc. is too long to get Hot water to the Taps / Shower quickly then the Secondary return pipework has to be run to tee into the Hot supply within the Bathroom / Kitchen etc. so that Hot water is available `instantaneously` at the Taps / Shower etc.

Having read what I wrote above it is not a particularly good description - but I cannot really explain any better than that.

Chris

 

[fezster]

However You MUST make sure that you Tee off the 35mm / 28mm in such a way that the Hot water is not being drawn form the return pipe.

Does a check valve, at where the return goes back into the cylinder, not prevent this anyway?

 

[CHRISX]

Does a check valve, at where the return goes back into the cylinder, not prevent this anyway?

Hello fezster,

Imagine a situation where the 15mm Secondary return is connected to a 35mm x 15mm x22mm tee.

I feel that when the 22mm draw off to a Bathroom is supplying water that there could easily be a slightly negative effect on the 15mm Secondary return and if that method of connecting a 15mm Secondary return was used [35 x 15 x 22] on a few draw off connections there could be a situation where the pressure / flow in the 15mm pipe would be slightly lowered and cavitation could occur at the Bronze Pump.

Although this is MY Theory and depends greatly on the pipework layout of the Hot water supply / Secondary return and the Hot water supply pressure etc. I would not want to take any chances that what I described could happen.

So I feel that extending the Hot water supply pipe size [If 35mm or 28mm] about a metre past the Hot water draw off points and then reducing down to 15mm would ensure that the 22mm draw off to Bathrooms or Kitchen [Sink - Washing machine - Dishwasher ?] did not have any slightly negative effect on the 15mm Secondary return.

When the 15mm Secondary return connects to a 22mm Hot water supply to a Bathroom or Kitchen [Sink - Washing machine - Dishwasher ?] within the Bathroom / Kitchen / near the Taps / outlets to give `instantaneous` Hot water there is not such a Volume of water difference at that connection so it should not cause any slight negative effect on the 15mm Secondary return.


Members may not agree with this theory - but I have never had any problems installing Hot water / Secondary return pipework in the way that I described - however I have encountered systems where problems did occur with Cavitation on Bronze Pumps and altering the Secondary return connection points to connect as I described here did solve the problems.


Chris

 

[Toxic Ted]

Make sure you insulate the cold as well as the hot and return.....there's nothing worse than brushing your teeth with warm water.